In recent years, touch panels have been widely used in smart phones, tablet-type portable terminals, and the like. There are a variety of different types of touch panels that are well-known, such as resistive touch panels, capacitive touch panels, and optical touch panels. Among these, projection-type capacitive touch panels, which can respond to multi-touch and in which touch locations can be detected with a high degree of accuracy, have become widely used. Hereafter, a touch panel will be described that is used in combination with a TFT liquid crystal display panel (hereafter sometimes referred to as a “TFT LCD”) that is used as a display panel. The display panel is not limited to a TFT LCD, and various types of display panels can be used, such as an organic EL display panel or an electrophoretic display panel.
There are various types of touch panels, such as external touch panels (in which the touch panel is disposed on the viewer side of a polarizing plate (referred to as a “front polarizing plate”) that is disposed on the viewer side of a display panel), on-cell touch panels, and in-cell touch panels. Here, an on-cell touch panel and an in-cell touch panel have been combined, forming a so-called “built-in touch panel”. Here, the word “cell” refers to a display cell (hereafter referred to as a “display panel”), and the liquid crystal display panel includes a pair of substrates (a TFT substrate and an opposite substrate, for example) that face each other through a liquid crystal layer and does not include a polarizing plate, for example. An on-cell touch panel includes a layer that functions as a touch panel between a polarizing plate and the opposite substrate of the liquid crystal display panel, while an in-cell touch panel includes a layer that functions as a touch panel on the liquid crystal layer side of the opposite substrate of the liquid crystal display panel or on the TFT substrate of the liquid crystal display panel. A built-in touch panel is useful in that the device (including the TFT liquid crystal display panel and the touch panel) is thinner, lighter, and narrower overall compared to an external touch panel, and also has the benefit of being able to increase light transmittance.
Patent Document 1 discloses a touch panel that is less likely to be affected by the potential of a user (a finger) since a common electrode of the liquid crystal display panel is used as driving electrodes (transmission electrodes) for a touch sensor. Patent Document 1 discloses an on-cell touch panel and an in-cell touch panel. FIG. 4 of Patent Document 1 discloses an on-cell touch panel that utilizes a vertical electric field mode (also referred to as “V mode”) liquid crystal display panel, for example. FIG. 9 and the like of Patent Document 1 disclose a touch panel that uses a fringe field switching (FFS) mode liquid crystal display panel that utilizes positive-type liquid crystal material as an example of an in-cell touch panel that utilizes a horizontal electric field mode (also referred to as “L mode”) liquid crystal display panel (see FIG. 10 of Patent Document 1).